???? ??? ??????? ???? ????? ??? ????? ???????? ??? ????? ?????????? ?? ????? ??????? ?? ????? ??????. ???? ????? ??? ?ficulties ???? ????? ??????? ? ??? ???? ???????. ?????? ?????? ????? ???? methods ????????? ????? ?????????? ???? ????. ???? ????? ??? ???? ??????? ????? ?????????? ?? ?????? ???